The present invention relates generally to an apparatus for testing the purity of precious metals, including gold, silver and platinum, and, more particularly, to a recalibration system that improves the operation and accuracy of the testing apparatus.
A precious metal testing apparatus is shown in U.S. Pat. No. 5,888,362, issued to Lloyd V. Fegan, Jr., on Mar. 30, 1999. This testing apparatus provides a portable device that can provide accurate analysis of the quality of the precious metal being tested by utilizing a hand-held probe having an electrode embedded in an electrolyte contained within a reservoir formed in the probe. The testing apparatus generates a galvanic current through the metal being tested from a battery, the strength of the current being proportionate to the quality of the precious metal being tested. In the Fegan patent, a meter circuit measures the extent of galvanic action of dissimilar metals in the presence of an electrolyte, one of the metals being the sample being tested for quality. Thus, the invention is useful for testing the metal content of coins, art objects jewelry, and the like, by reason that the probe can simply be touched against the object being tested to provide a reading representing the quality of the precious metal in the object.
The hand-held probe in the aforementioned precious metal testing apparatus is typically in the form of a pen having a fibrous tip from which a small amount of electrolyte is deposited onto the object being tested. The meter attached to the probe continuously measures the strength of the galvanic current and compares the result with a known point of reference for the type of precious metal being tested, whereby the percentage of precious metal within the object being tested will be know. This measurement process by the meter and pen is completed within a few hundredths of a second, thus providing an efficient manner in which the quality of precious metal can be determined. However, even though the measurement process is fast, the strengths of the galvanic reaction when reacted with gold, silver or platinum are very weak.
Accordingly, slight variations in system parameters are significant enough to reduce the overall accuracy of the meter, and can render the testing apparatus essentially useless. In addition to the electronic and mechanical variations that affect the accuracy of the testing apparatus, variations in operating environment, such as temperature and humidity, also affect the accuracy of the meter. One skilled in the art will recognize that with any galvanic reaction occurring from dissimilar metals and an electrolyte one metal is sacrificed to the other across the electrolyte. As the electrolyte and the sacrificial metal are consumed, the galvanic strength varies. Furthermore, the accuracy of the testing apparatus is impacted negatively over time because the strength of the galvanic reaction decreases with each and every specimen measured. The exhaustion of materials within the pen that are responsible for generating the galvanic strength can be mitigated by replacing an improperly functioning pen probe with a new pen probe. When the pen is replaced, however, the replacement pen will have subtle differences in composition from the pen that has been replaced, which again provides a variation that impacts the accuracy of the testing apparatus.
Calibrating the Fegan precious metal testing apparatus was possible by removing the housing and utilizing a screwdriver or similar instrument to adjust one of the variable resisters in the Fegan circuitry. Testing against a known purity of gold would provide a calibrated reading that would often need further calibration, again requiring the removal of the meter housing and further adjustment of one of the variable resisters. This process was repeated until the Fegan precious metal testing meter was showing the proper results from the known purity sample being tested for the purposes of calibrating the meter. Thus, calibrating the Fegan meter was a complex and time consuming process. Accordingly, accuracy in testing precious metals with the Fegan meter was not consistent as changes in the electrolyte and other environmental factors would deteriorate accurate test results.
A solution for solving the accuracy issues of the aforementioned testing apparatus would be desirable. One possible solution could be a method for recalibrating the testing apparatus to increase accuracy and improve the usable life of the testing apparatus across various manufacturing differences, operating environments, pen replacements, and the number of objects being tested.